Genetic population structure of Sphaeroma wadai Nunomura, 1994 (Isopoda: Sphaeromatidae) along the Japanese coast

抄録

DNA sequences from a portion of the mitochondrial 16S rRNA gene were used to examine genetic differentiation among the local coastal populations of the Japanese wood-boring isopod Sphaeroma wadai Nunomura, 1994. Of the 15 haplotypes identified, only 3 were shared among the sampled localities. The most dominant haplotype was shared by all populations from the Japanese mainland. All haplotypes identified from Okinawa Island and Iriomote Island were endemic to each island. For the Japanese mainland group, the haplotype network showed a star-like shape, with rare haplotypes radiating from the central most common haplotype by only one or two mutation steps. Haplotypes identified from Iriomote Island were separated by many steps from those identified from all other sampled localities, and haplotypes identified from Okinawa Island were separated by several steps from those identified from the Japanese mainland. Phylogenetic analyses revealed the existence of two lineages: one comprising specimens from Iriomote Island and the other comprising specimens from the Japanese mainland and Okinawa Island. These two lineages diverged at an uncorrected p-distance of 9.1%–10.3%, probably representing a different species. There were no clear morphological differences between the two lineages except for the propodus length of the seventh pereopod of male individuals.